A printing cylinder support unit of this type is known from EP 0 864 421 A1. This document discloses a printing machine with exchangeable ink-applicator means. A printing machine of this type comprises a plurality of printing units, wherein each printing unit performs a separate function in the overall printing process. Printing units of this type may be suitable for various different printing forms with different pattern repeat lengths and suitable for various printing techniques, such as rotary screen printing, intaglio printing, letter press printing and flexographic printing. A printing unit generally comprises a printing cylinder and ink-applicator means. In the operating state, the printing cylinder makes contact along a describing line on the surface of the cylinder, the contact line, with a substrate which is to be printed. Ink is applied via the ink-applicator means to the inner side, in the case of screen printing, and directly to the outer side, in the case of printing techniques other than screen printing, of the printing cylinder.
The printing cylinder rests rotatably at each of the two axial ends in a circumferential bearing system, comprising three support rollers which radially enclose a round bearing ring which is secured concentrically on the corresponding axial end of the printing cylinder. This position is known as the retaining position. One of the three rollers is situated at the location of the contact line. The other two rollers are situated at the other end of the bearing ring.
In the prior art, it is possible to exchange printing cylinders. The reason for changing a printing cylinder may be that a different pattern repeat length and/or a different printing pattern has to be printed. It is advantageous for a printing cylinder with a different diameter and/or printing image to be used for this purpose. A printing cylinder can also be changed in order to change the printing technique. To exchange a printing cylinder, it is possible for two support rollers to move outwards along a path which is diagrammatically indicated by arrows A in FIG. 11 of the above mentioned patent. It is known in practice that paths A of this type are produced, for example, on account of the support rollers being rotatably secured to pivot arms, it being possible for the pivot pin of each of the pivot arms in its entirety to be moved in rectilinear translation if appropriate.
The third support roller for the radial retaining is located at a fixed position, where this roller, in the retaining position, makes contact with the bearing ring at a reference point. In the operating state, this reference point is located at a fixed position with respect to the contact line. On account of the position of this fixed roller, printing cylinders which have different diameters nevertheless make contact with the substrate along the same contact line.
This known printing cylinder support unit has a significant drawback. In practice, it has been found that the presence of a fixed support roller at the location of the reference point constitutes a serious restriction in terms of allowing the known support unit to be used in printing machines which do not take account of this fixed support roller and in which there is insufficient space for a fixed roller of this nature. The known support unit cannot then be used.